Thicker than Water (Tech Trends Feature)

In the field of fluid dynamics, blood falls under the non-Newtonian category because its behavior defies the classic Newtonian principle that governs water's movement. In other words, with blood, the rate of shear is not proportional to the corresponding stress (McGraw-Hill Dictionary of Scientific and Technical Terms, McGraw-Hill Companies, 2003).

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It was up to Don Novkov, Luminous Medical's senior mechanical engineer, to figure out how blood behaves when it trickles into an automated glucose-measurement device, the premier product from Luminous. A veteran SolidWorks user, Novkov found that COSMOSFloWorks, a computational fluid dynamics (CFD) analysis program for SolidWorks users, had precisely what he needed to deconstruct the non-Newtonian flow.

The Inconspicuous Poke

Currently still in development, Luminous' glucose-measurement system is intended for hospital patients in intensive care, intermediate care, and operating rooms. "A device like this has never been on the market before, so we're hoping to be the first," Novkov revealed. Luminous was founded specifically to create the product.

"The common method used today is the finger-sticking method," Novkov added. "As you might gather from the name, this requires that a nurse comes in,pokes the patient'sfinger with a handheld device, reads thechemical content ofthe patient's blood, then records it."

For patients who must avoid hypoglycemia, or low blood glucose, the process has to be repeated as frequently as every 30 to 60 minutes ("The Glycemic Control in the Critically Ill and Injured Patient: Progress and Problems," Webcast, November 2, 2006, Society of Critical Care Medicine, www.sccm.org). By contrast, Luminous' device is attached to a catheter, the standard ICU accessory for automatically monitoring a patient's vital signs and delivering drugs and regular insulin doses (figure 1).

Figure 1. The Luminous Medical Glucose Measurement System incorporates an accessory device pole (where the saline bag is hanging from the catheter) from which infusion pumps are mounted. The company points out that this design minimizes the device's floor-space requirements.

"Our device draws a small amount of blood through the infusion tube attached to the catheter," Novkov said. "When it reaches the device, it flows into the flow cell. The device then shines infrared light through that flow cell to determine the glucose volume in the blood."

In its online literature, Luminous points out that "the net result is a system that accurately and precisely reports patient glucose readings without the need for frequent calibration and allows for automated, frequent measurements."

"The patients in the ICU don't really notice the catheter," Novkov said. "They're hooked up to one for the most part, so [measuring glucose from the catheter] doesn't present additional discomfort. On the other hand, if the nurse comes in with a handheld device, they can't help but think, 'I'm getting my finger stuck again.'"

The Non-Newtonian Discovery

Twelve years ago, Novkov began using SolidWorks for his CAD work when he worked at Inventive Technologies, a respiratory-device maker later acquired by Respironic (itself now pending acquisition by Phillips Electronics). At Luminous Medical, he and his colleagues used the same software to design the 400-part assembly that comprises the new glucose-measuring system (figure 2, p. 14).

Figure 2. Luminous Medical's glucose-measuring system was designed in SolidWorks, making it ideal for downstream analysis in COSMOSFloWorks, a computational fluid dynamics analysis program for SolidWorks users.

To simulate and study how blood would flow into the flow cell, Luminous' engineering team used the COSMOSFloWorks CFD program for SolidWorks. The program features non-Newtonian fluid flow, precisely what Novkov needed to study blood flow in the device.

COSMOSFloWorks is intended for the valve/regulator, medical, electronics, and oil and gas industries, among others. The software analyzes conjugate heat transfer; subsonic, supersonic, and compressible flows; mixing of gases; flow around rotating geometry; porous media; cavitation; humidity and climate control; fluid structure interaction; and more. With the release of COSMOSFloWorks 2008, the company expanded its engineering database for both Newtonian and non-Newtonian liquids. The non-Newtonian additions include applesauce, blood, olive oil, polyethylene, polystyrene, and slurries (figure 3).

Figure 3. COSMOSFloWorks lets users simulate and model the flow patterns of non-Newtonian fluid such as blood, toothpaste, or paint. The image here shows the simulated flow of molten plastic through an extrusion channel under high pressure.

"Non-Newtonian flow is so complicated that you're bound to need software to figure it out," Novkov remarked. "It's one of the reasons we bought the software. In fact, I'm sure we would not have bought [COSMOSFloWorks] if [non-Newtonian flow] weren't in the feature list."

At one point, the engineers noticed something odd about the blood flow inside the device, as revealed by COSMOSFloWorks. "It was a flow that had a nonuniform profile," recalled Novkov. "That would make it difficult for the flow cell to wash out the saline fluid [pumped in behind the blood], which in turn would make the spectroscopic reading less accurate."

Novkov's engineering instinct told him he would have to modify the geometry of the flow path leading to the cell to get a better distribution model. It took him three or four iterations to get the correct velocity and circulation.

Temperature Watch

After the device has measured the glucose content of the blood, the blood within the flow cell is pumped back into the patient. Therefore, it is critical to ensure the infrared light doesn't raise the temperature of the blood.

"We performed tests of the device instrumented with thermistors and measured no significant temperature increase, so we were fairly certain the process wouldn't heat up the blood," Novkov said. "But we didn't want to take chances. We wanted to validate it. We didn't buy COSMOSFloWorks for that purpose. Since we had the software, we decided we should run the analysis and generate a report."

Through the use of COSMOSFloWorks, Novkov and his colleagues were able to perform a heat-transfer analysis to ascertain that no significant heat would be imparted to the blood through the device's operation.

The software, observed Novkov, "is fairly user friendly. The interface with SolidWorks was seamless. You don't have to pay a lot of attention to generating meshes. I put the software to use with only a few tweaks to the default parameters."

A fluid dynamics veteran, Novkov can recall the times when he had to manually calculate the operations now automatically performed by COSMOSFloWorks. Leaving the complex calculation tasks to the software is "a pleasure," he said.

The Luminous Medical Glucose Measurement System, as the product is now known, is in preproduction, pending U.S. Food and Drug Administration review.

About the Author: Kenneth Wong

Autodesk Technical Evangelist Lynn Allen guides you through a different AutoCAD feature in every edition of her popular "Circles and Lines" tutorial series. For even more AutoCAD how-to, check out Lynn's quick tips in the Cadalyst Video Gallery. Subscribe to Cadalyst's free Tips & Tools Weekly e-newsletter and we'll notify you every time a new video tip is published. All exclusively from Cadalyst!Follow Lynn on Twitter

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